Synthesis and Structure of a New Ternary Silver-Rich Sulfide BaAg8S5

A new ternary silver-rich sulfide, BaAg8S5, was synthesized. This solid-state compound crystallizes in the monoclinic, centrosymmetric space groupP21/mwitha=7.6720(2) ?,b=17.6660(4) ?,c=8.9370(2) ?,BETA=107.890(1)°,Z=4, andV= 1152.70(5) ?3. The refinement results areR1=0.0490 and wR2=0.1136 forI>2SIGMA(I) using 2552 reflections and 137 parameters. As in the binaryALPHA-Ag2S andBETA-Ag2S solids, the coordination geometry of both Ag and S is complex. However, if only the bonding of Ag to S is concerned, the arrangement is simple. Ag of the first type is connected to two S atoms in both linear and bent fashions. Ag of the second type is coordinated to three S atoms in a pyramidal shape. The structure can be viewed as a three-dimensional network formed by Ag and S atoms with Ba atoms occupying channels parallel to thecaxis. Theoretical analysis using the extended Hückel method indicates that the solid should be a semiconductor.